Vertical probe assembly with air channel

ABSTRACT

A vertical probe assembly includes an upper die; a lower die; a plurality of probes, the probes comprising an electrically conductive material, wherein the probes extend from the upper die through the lower die; and an air channel located between the upper die and the lower die, such that airflow through the air channel passes through the plurality of probes.

BACKGROUND

This disclosure relates generally to the field of semiconductor devicetesting, and more particularly to a vertical probe assembly forsemiconductor device testing.

Semiconductor devices, also referred to as integrated circuit (IC)chips, are electrically interconnected for such purposes as testing,burn-in, and utilization. Interconnection methods include rigid probesand contacts, flexible probes and contacts, wire bonding, soldering, andwelding. The topology of the interconnections on a chip may vary from aline or linear array of peripherally spaced pads, bumps, or contacts, toan area array of two dimensionally spaced pads or bumps. The pads ofbumps in either a linear or area array normally have a uniform width andcenter-to-center spacing in the array. The array of contacts in an areaarray are usually arranged in a pattern such as rows and columnsorthogonal to one another. The trend in IC chips is for denser arrays ofcontacts and for more contacts per chip.

IC chips are typically tested at the wafer level, before the wafer isdiced into individual IC chips. At the wafer level more than one chipmay be tested at one time. In some cases individual chips are tested andburned in. In order to make temporary contact with high-density arraysof contacts on many IC chips sequentially at relatively high speeds fortesting or burn-in of the IC chips, a probe assembly may be used. Onetype of probe assembly used for this purpose is a vertical probeassembly. An example of a vertical probe assembly is described in U.S.Pat. No. 4,027,935, which was granted on Jun. 7, 1977 to Byrnes et al.,and which is herein incorporated by reference in its entirety. Avertical probe assembly has a plurality of conductive probe wires(referred to hereinafter as probes) mounted in parallel, with the endsof the probes ending in a plane transverse to the axis of the wires. Theprobe ends are shaped to facilitate making electrical contact to thecontacts of an IC. Each probe is sufficiently rigid to apply pressure toa corresponding contact on the IC to form good electrical contact, yetflexible or springy enough to prevent excessive pressure on ordeformation of the contact. When the probes in the probe assembly arealigned correctly, the ends are floating and the cumulative pressureexerted by the probes is sufficient with respect to the area of thecontacts to form electrical connections with all of the contacts on theIC. Insufficient pressure may result in a lack of electrical contactwith some contacts on the IC, while excess pressure from the verticalprobe assembly on the contacts may damage the IC.

During testing or burn-in of an IC using a vertical probe assembly, theprobes in the vertical probe assembly and contacts on the IC mayexperience relatively high currents caused by high test or burn involtages. The high currents can cause overheating and may damage thevertical probe assembly or the IC. Faulty contacts discovered duringburn-in or testing may be incorrectly attributed to a failure in the ICitself, instead of to an error with the vertical probe assembly, and anIC that contains a faulty contact may be discarded without furthertesting. This may lead to reduced yield for a semiconductormanufacturing process.

BRIEF SUMMARY

In one aspect, a vertical probe assembly includes an upper die; a lowerdie; a plurality of probes, the probes comprising an electricallyconductive material, wherein the probes extend from the upper diethrough the lower die; and an air channel located between the upper dieand the lower die, such that airflow through the air channel passesthrough the plurality of probes.

In another aspect, a method of using a vertical probe assembly includescausing airflow to flow through an air channel in the vertical probeassembly, the air channel being located between an upper die and a lowerdie of the vertical probe assembly, the vertical probe assembly furthercomprising a plurality of probes, the probes comprising an electricallyconductive material and extending from the upper die through the lowerdie, and wherein the airflow through the air channel passes through theplurality of probes.

Additional features are realized through the techniques of the presentexemplary embodiment. Other embodiments are described in detail hereinand are considered a part of what is claimed. For a better understandingof the features of the exemplary embodiment, refer to the descriptionand to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1A is a cross sectional view illustrating an embodiment of avertical probe assembly with an air channel.

FIG. 1B is an isometric cross sectional view illustrating an embodimentof a vertical probe assembly with an air channel.

FIG. 1C is a bottom view illustrating an embodiment of a vertical probeassembly with an air channel with the lower die removed.

FIGS. 2A-B are flowcharts illustrating embodiments of methods of using avertical probe assembly with an air channel.

DETAILED DESCRIPTION

Embodiments of a vertical probe assembly with an air channel, and amethod of using a vertical probe assembly with an air channel, areprovided, with exemplary embodiments being discussed below in detail. ICtesting and burn-in using a vertical probe assembly is limited by theamount of current that may be carried per probe, as the probes mayoverheat at higher currents, resulting in damage to the contacts on theIC, the probes, or the vertical probe assembly. Therefore, a verticalprobe assembly may include an air channel between an upper die and alower die of a vertical probe assembly. Airflow may be forced throughthis air channel across the probes. This may cool the probes, preventingdamage to the vertical probe assembly and to the IC under test whileallowing higher current per probe to be applied to the IC under test insome embodiments. In various embodiments, the airflow in the air channelmay comprise any appropriate gas or dielectric liquid, including but notlimited to ionized air, nitrogen gas, or liquid nitrogen.

Additionally, in other embodiments involving IC testing that isperformed at a specified temperature, probes are typically soaked beforethe start of testing, otherwise alignment between the probe array and ICunder test may shift as testing proceeds and the probe temperatureapproaches the test temperature. Probe soak time adds time and expenseto the testing process because no IC is actually being tested during theprobe soak step. Therefore, to obviate the need for probe soaking, airmay be forced through the air channel that is at a specifiedtemperature, such that the probes are brought to the test temperaturerelatively quickly at the start of the testing. This prevents heattransfer between the IC and the probes during testing, which may affectthe alignment of the contacts on the IC and/or the probes. Thetemperature of the air that is forced through the air channel may be thesame as the test temperature in some embodiments. The testing may betesting at an elevated temperature in some embodiments, and the air thatis forced through the air channel may be heated air.

The probes extend through the upper and lower dies of the vertical probeassembly, and the air channel comprises a gap between upper and lowerdies. Airflow may be forced through the air channel across the probes.One or more holes may be provided in the upper die or lower die for theair inlet and/or outlet. The speed, volume, and temperature of theairflow may be controlled based on the testing or burn-in conditions.The airflow through the channel may be provided by compressed air and/ora vacuum in various embodiments.

The probes in a vertical probe assembly have a current limit, i.e., amaximum amount of current that may be conducted in the probe withoutdamage to the probe or an IC that is contacted by the probe. The centerarea of the probe may overheat due to excessive current; which mayresult in a loss of spring rate, height, force or electrical resistanceon the affected probes. The amount of current needed per probe duringtesting or burn-in increases as chip power during regular usageincreases. Some chips may also need to be stress tested to ensure thatthe chip will stand up to a wide variety of operating conditions. Stresstesting may include usage of a vertical probe assembly at elevatedcurrents, temperatures, voltages, and/or frequencies. Addition of theair channel between the upper and lower die increases the current limitof the vertical probe assembly by dissipating the heat that builds upduring use of the probe. A probe's current limit may be significantlyincreased with even relatively small airflow across the probe throughthe air channel. The air channel therefore allows for testing or burn-inunder a relatively wide range of conditions without damage to the IC orthe vertical probe assembly. Increasing the probe current limit alsomeans fewer probes are required to test a given device, resulting insignificant cost savings and reduced probing force.

FIG. 1A is a cross sectional view illustrating an embodiment of verticalprobe assembly 100. Vertical probe assembly 100 includes an air channel109 located between an upper die 105 and a lower die 108. Vertical probeassembly 100 further includes a stiffener 103, a printed circuit board104, a substrate 107, and probes 106. The probes 106 extend from thesubstrate 107, through the upper die 105, through the air channel 109,and through the lower die 108 to the bottom of the vertical probeassembly 100. The probes 106 may comprise any appropriate number ofconductive wires. The upper and lower dies 105 and 108 may be plastic,ceramic, or silicon in various embodiments. The substrate 107 comprisesa space transformer and may be ceramic, organic, or silicon in variousembodiments. The substrate 107 may also be incorporated directly intothe printed circuit board 104; in such an embodiment the substrate 107is referred to as a footprint on board. The substrate 107 may also beincorporated into the upper die in some embodiments. The stiffener 103may also be incorporated directly into the printed circuit board 104 insome embodiments. The probes 106 make contact with contacts on an ICthat is located below the probes 106 of the vertical probe assembly 100during testing or burn-in; the IC may be held in place by a vacuum insome embodiments. The IC may be part of a wafer 111 that includes aplurality ICs, as shown in FIG. 1A. The probes 106 may be used to testthe plurality of ICs on the wafer 111 before the wafer is diced intoindividual ICs. The wafer 111 may be supported by a wafer chuck 112during testing of the ICs on the wafer 111 using the probes 106. Thewafer chuck 112 may comprises a rigid support for the wafer 111, and maybe copper in some embodiments. Air channel 109 is located between theupper die 105 and the lower die 108, and airflow through the air channel109 passes through the probes 106.

The air channel 109 of FIG. 1A is shown with an air inlet 101 and airoutlet 102; these are shown for illustrative purposes only. In someembodiments, the air outlet of an air channel 109 may be located on topof the upper die 105 at alternate air outlet 110 instead of at airoutlet 102. Air inlet 101 and alternate air outlet 110 comprise holesthat are formed in the top of the upper die 105, and air outlet 102comprises a hole in the side of the vertical probe assembly 100. Inadditional embodiments, the air inlet or outlet may comprise a holethrough the lower die 108, which may be located, for example, underneathair outlet 102. Airflow in air channel 109 is indicated by arrows inFIG. 1A, which are also shown for illustrative purposes only. Theairflow may flow in the opposite direction as is indicated by the arrowsin air channel 109 in some embodiments. The airflow may be provided bycompressed air or a vacuum. The compressed air or vacuum that causes theairflow in air channel 109 may be provided at the air inlet 101, airoutlet 102, or alternate air outlet 110 in various embodiments.Compressed air enables relatively high flows at a more controlledtemperature, while a vacuum may provide a self cleaning action to theprobes 106. In some embodiments, a positive pressure (i.e., compressedair) may be applied at air inlet and while a negative pressure (i.e., avacuum) is also be applied at the air outlet. In various embodiments,the airflow in the air channel 109 may comprise any appropriate gas ordielectric liquid, including but not limited to ionized air, nitrogengas, or liquid nitrogen. Additionally, in some embodiments, air may flowfrom the air channel 109 thru the holes in the upper and/or lower dies105/108 through which the probes 106 extend.

The vertical probe assembly 100 of FIG. 1A is shown in further detailwith respect to FIGS. 1B-C. FIG. 1B is an isometric cross sectional viewillustrating the vertical probe assembly 100 with an air channel 109,and FIG. 1C is a bottom view illustrating the vertical probe assembly100 with an air channel 109 with the lower die 108 removed.

FIGS. 2A-B are flowcharts illustrating embodiments of methods of using avertical probe assembly with an air channel, such as vertical probeassembly 100 of FIGS. 1A-C. FIG. 2A relates usage of the air channel todissipate heat that is built up around the probes inside the verticalprobe assembly from current flow in the probes during testing, whileFIG. 2B relates to elimination of a probe soak step for testing that isperformed using the vertical probe assembly at a specified temperature.

Turning to FIG. 2A, a method 200A for using a vertical probe assemblysuch as vertical probe assembly 100 of FIGS. 1A-C having an air channel109 is shown. FIG. 2A is discussed with reference to FIGS. 1A-C. Inblock 201A, the probes 106 of the vertical probe assembly 100 arecontacted to contacts on an IC. The IC may be held in place by a vacuumin some embodiments. In other embodiments, the IC may be part of awafer, such as wafer 111 as shown in FIG. 1A, that includes a pluralityof ICs, and that is held in place by a wafer chuck 112. Then, in block202A, current is applied to the contacts on the IC via the probes 106.The current in the probes 106 causes heat to build up around the probes106 inside the vertical probe assembly 100 between the upper die 105 andthe lower die 108. Then, in block 203A, air is forced through the airchannel 109 to dissipate the heat around the probes 106 that is built upbetween the upper die 105 and the lower die 108 of the vertical probeassembly 100 during the testing or burn-in. In some embodiments, theairflow through air channel 109 may commence before the IC is contactedto the probes 106 and current is supplied to the IC via the probes 106.The speed, volume, and temperature of the airflow in air channel 109 maybe controlled based on the testing or burn-in conditions. The airflowthrough the air channel 109 may be provided by compressed air and/or avacuum in various embodiments, and may be applied at any appropriatelocation with respect to the air channel 109 in various embodiments. Invarious embodiments, the airflow in the air channel may comprise anyappropriate gas or dielectric liquid, including but not limited toionized air, nitrogen gas, or liquid nitrogen. Lastly, in block 204A, inembodiments in which the vertical probe assembly 100 is used inconjunction with ICs on a wafer before dicing of the wafer, the verticalprobe assembly 100 is used to test or burn-in the plurality of ICs onthe wafer, and after testing or burn-in using the vertical probeassembly 100 is completed, the wafer is diced into individual ICs. ICson the wafer that were determined to be faulty may then be discarded.

Turning to FIG. 2B, a method 200B for using a vertical probe assemblysuch as vertical probe assembly 100 of FIGS. 1A-C having an air channel109 across the probes is shown. FIG. 2B is also discussed with referenceto FIGS. 1A-C. In block 201B, air having a specified temperature isforced through the air channel 109 to bring the vertical probe assembly100 including probes 106 and upper die 108 to a steady state temperaturethat will not fluctuate significantly, thereby ensuring stable alignmentbetween the probes 106 and the IC during testing. The speed, volume, andtemperature of the airflow in air channel 109 may be controlled based onthe testing conditions. The airflow through the air channel 109 may beprovided by compressed air and/or a vacuum in various embodiments, andmay be applied at any appropriate location with respect to the airchannel 109 in various embodiments. In various embodiments, the airflowin the air channel may comprise any appropriate gas or dielectricliquid, including but not limited to ionized air, nitrogen gas, orliquid nitrogen. Then, in block 202B, testing of an IC is performedusing the vertical probe assembly 100 with the probes 106 at the testtemperature. During the testing current is applied to the contacts on anIC that are contacted to the probes 106 via the probes 106. In someembodiments, the IC may be part of a wafer, such as wafer 111 as shownin FIG. 1A, that includes a plurality of ICs, and that is held in placeby a wafer chuck 112. Lastly, in block 203B, in embodiments in which thevertical probe assembly 100 is used in conjunction with ICs on a waferbefore dicing of the wafer, the vertical probe assembly 100 is used totest a plurality of ICs on the wafer, and after testing using thevertical probe assembly 100 is completed, the wafer is diced intoindividual ICs. ICs on the wafer that were determined to be faulty maythen be discarded.

For an example vertical probe assembly having an air channel between theupper die and the lower die, the probe current limit may besignificantly increased as compared to a vertical probe assembly withoutsuch an air channel, especially for a vertical probe assembly having arelatively large number of densely-arrayed probes for contacting ICshaving similarly densely-arrayed contacts, as such a configuration mayhave significant heat buildup inside the vertical probe assembly. Theincrease in the current limit may be about 200% for an example verticalprobe assembly that includes single probe, or up to about 400% for anexample vertical probe assembly that includes an array of 3000 probes.

The technical effects and benefits of exemplary embodiments include avertical probe assembly having a relatively high current limit andelimination of the need for presoaking.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A vertical probe assembly, comprising: an upper die; a lower die; aplurality of probes, the probes comprising an electrically conductivematerial, wherein the probes extend from the upper die through the lowerdie; and an air channel located between the upper die and the lower die,such that airflow through the air channel passes through the pluralityof probes.
 2. The vertical probe assembly of claim 1, wherein the airchannel comprises an air inlet comprising a hole located in one of theupper die and the lower die.
 3. The vertical probe assembly of claim 2,further comprising compressed air located at the air inlet, thecompressed air being configured to cause the airflow in the air channel.4. The vertical probe assembly of claim 1, wherein the air channelcomprises an air outlet comprising a hole located in one of the upperdie and the lower die.
 5. The vertical probe assembly of claim 4,further comprising a vacuum located at the air outlet, the vacuum beingconfigured to cause the airflow in the air channel.
 6. The verticalprobe assembly of claim 1, further comprising compressed air located atan air inlet of the air channel and a vacuum located at an air outlet ofthe air channel, the compressed air and the vacuum being configured tosimultaneously cause the airflow in the air channel.
 7. The verticalprobe assembly of claim 1, further comprising a current flowing throughthe probes to a plurality of contacts located on an integrated circuit,wherein the airflow is configured to dissipate heat that is caused bythe current from between the upper die and the lower die inside thevertical probe assembly.
 8. The vertical probe assembly of claim 1,wherein the airflow is configured to bring the probes to a specifiedtest temperature for testing of an integrated circuit.
 9. The verticalprobe assembly of claim 1, wherein the airflow in the air channelcomprises one of ionized air, nitrogen gas, and liquid nitrogen
 10. Thevertical probe assembly of claim 1, wherein the probes further extendthrough the upper die and make contact to a space transformer that islocated on top of the upper die.
 11. A method of using a vertical probeassembly, the method comprising: causing airflow to flow through an airchannel in the vertical probe assembly, the air channel being locatedbetween an upper die and a lower die of the vertical probe assembly, thevertical probe assembly further comprising a plurality of probes, theprobes comprising an electrically conductive material and extending fromthe upper die through the lower die, and wherein the airflow through theair channel passes through the plurality of probes.
 12. The method ofclaim 11, wherein the air channel comprises an air inlet comprising ahole located in one of the upper die and the lower die.
 13. The methodof claim 12, further comprising compressed air located at the air inlet,the compressed air being configured to cause the airflow in the airchannel.
 14. The method of claim 11, wherein the air channel comprisesan air outlet comprising a hole located in one of the upper die and thelower die.
 15. The method of claim 14, further comprising a vacuumlocated at the air outlet, the vacuum being configured to cause theairflow in the air channel.
 16. The method of claim 11, furthercomprising compressed air located at an air inlet of the air channel anda vacuum located at an air outlet of the air channel, the compressed airand the vacuum being configured to simultaneously cause the airflow inthe air channel.
 17. The method of claim 11, further comprising acurrent flowing through the probes to a plurality of contacts located onan integrated circuit, wherein the airflow is configured to dissipateheat that is caused by the current from between the upper die and thelower die inside the vertical probe assembly.
 18. The method of claim11, wherein the airflow is configured to bring the probes to a specifiedtest temperature for testing of an integrated circuit.
 19. The method ofclaim 11, wherein the airflow in the air channel comprises one ofionized air, nitrogen gas, and liquid nitrogen
 20. The method of claim11, wherein the probes further extend through the upper die and makecontact to a space transformer that is located on top of the upper die.